Slightly less big brother

The vast police directory is trimmed, but only a little

AT THE start of the 20th century, Scotland Yard's fingerprint bureau began a quiet revolution in policing. A hundred years on, detectives have a new tool at their disposal in the form of DNA matching. In 1995 the government set up a national database recording the DNA of everyone who was convicted of a crime, hoping that it would make future cases easier to crack. Since then the England and Wales database has swollen to 5.5m entries, covering 4.8m citizens (some profiles are duplicates), or some 9% of the population. It is thought to be the biggest DNA database in the world. Despite plans announced this week to limit its growth, it looks likely to stay that way.

The reason for the database's size is that since 2004 it has included not just those convicted of crimes but those who have been merely arrested. As far as police are concerned, the bigger the pool, the more chance of a match with their next crime scene. But the inclusion of people who have never committed a crime has been controversial. Up to a million of those in the database do not have a conviction. Chief constables have the discretion to remove profiles if they choose, but that seldom happens. One MP, Diane Abbott, is running surgeries to show her constituents how to appeal. Still, only a few hundred profiles are deleted each year.

Last December the European Court of Human Rights ruled that holding so many innocent people's DNA records “could not be regarded as necessary in a democratic society”. On November 11th the Home Office released plans to trim the number of people being included—a bit. People arrested and released will still have their DNA held, but only for six years. Under-18s in the same situation will stay on the database for three years.

As is now customary, the plans include tougher rules on terrorism: those cleared of terror offences could still have their DNA held indefinitely, subject to regular reviews. And the Home Office proposes to give the police the power to take DNA from people who have convictions pre-dating the database. No one knows how many are in this group, but the back catalogue could inflate the database dramatically. Chris Sims, the chief constable with responsibility for the database, expects forces to use the power “proactively”.

Whether the European Court will be satisfied with these tweaks remains to be seen. The opposition Conservatives say that if they win power at the approaching general election they will copy the Scottish system, in which people who are not convicted usually have their DNA removed from the database as soon as the case against them is dropped. Keeping the records of those who have done nothing wrong undermines the traditional presumption of innocence, the Tories say.

The government argues that shrinking the pool of people on the database means that fewer crimes will be solved. The Association of Chief Police Officers examined a set of homicide and rape cases from last year in which a DNA match had been made with a profile on the national database. In about a tenth of these cases, the match was with someone who was on the database despite not having a conviction.

Home Office boffins justify the six-year retention of innocents' DNA with research showing that people who are let off after an arrest are more likely than the general public to be rearrested. Their likelihood of rearrest only drops back to average levels after six years, the number-crunchers found. (Interestingly, juveniles take longer to return to a “normal” risk profile than adults, leading Home Office scientists to note that there is a case for retaining their DNA for longer than that of adults, not shorter, as the government has decided.)

High profile cases have made even liberal-minded folk think twice about limiting the size of the database. Last year Mark Dixie was jailed for a rape and murder that might never have been solved had he not had a DNA sample taken following his arrest (and subsequent release) over a pub brawl a few months later. The prospect of even a handful of killers evading justice will make it hard for any government to cut the database back much more.